Fuel nozzle assemblies for gas turbine engines have included dual orifice, airblast and hybrid types for the purpose of discharging one or more atomized fuel sprays into the combustors of gas turbine engines. In the case of dual orifice and hybrid types of fuel nozzle assemblies, a primary fuel spray and a secondary fuel spray are discharged by the nozzle. The primary fuel spray is typically a low fuel flow rate spray for the purpose of low power engine operation while the secondary fuel spray is a high fuel flow rate spray used in addition to the primary fuel flow spray for the purpose of high power engine operation. The secondary fuel flow typically is valved by a fuel metering valve integrally disposed in the support housing of the fuel nozzle assembly. U.S. Pat. No. 3,662,959 issued May 16, 1972, and U.S. Pat. No. 4,491,272 issued Jan. 1, 1985, illustrate typical dual orifice fuel nozzle assemblies with integral secondary fuel metering valving.
In some airblast fuel nozzle assemblies, a single fuel spray is injected into the combustor. The fuel spray flow rate typically is valved by a fuel metering valve integrally disposed in the support housing of the assembly Such airblast fuel nozzle assemblies are employed on the F100 military aircraft gas turbine engine.
In the past, the various components of the fuel nozzle assembly have been assembled onto a single support housing, typically comprised of a single metal casting or forging, having a chamber adjacent the upstream end to receive a fuel metering valve cartridge and a fuel filter and having a downstream end onto which the fuel nozzle is attached. In particular, the fuel injection nozzle is typically formed of concentric members, some of which are attached, for example, brazed or welded, to the downstream end of the support housing and others of which are pre-brazed/welded together. That is, a functioning nozzle is only formed once all the concentric components are fabricated to one another and to the downstream end of the support housing. A stand-alone, functioning nozzle module having its own support housing without any fuel metering valve chamber has not been employed heretofore.
Similarly, although a metering valve cartridge has been employed, the valve cartridge is assembled into the chamber adjacent the upstream end of the support housing (the same support housing on which the nozzle is attached) and enclosed in the chamber by the end closure cap sealed/welded on the upstream end of the support housing, the end closure cap typically having a fuel inlet thereon. A standalone, functioning valve module having its own support housing with a fuel inlet has not been employed heretofore.
Furthermore, subsequent repair of these fuel nozzle assemblies after service in the gas turbine engine is complex, time-consuming and costly, especially when the nozzle requires repair or replacement for some reason. In particular, the various concentric members forming the nozzle must be disassembled from the downstream end of the support housing and repaired or replaced and require subsequent reattachment (e.g., brazing, welding) to one another and to the support housing to form a functioning nozzle.
Fuel nozzle assemblies incorporating a fuel metering valve are calibrated to exhibit fuel flow versus fuel pressure characteristics within prescribed limits; e.g., within plus or minus a certain percentage (e.g., 3%) of the prescribed nominal fuel flow versus fuel pressure characteristics (or flow curve) prescribed for a particular engine application. For example, the fuel metering valve cartridge is precalibrated using a test adapter to simulate downstream pressure drops (or back pressure) to be encountered when the valve cartridge is assembled inside the support housing. The fuel injection nozzle components are attached, for example, brazed, on the support housing to form a functioning nozzle and then the nozzle is flow tested without the valve cartridge disposed in the support housing. If necessary, a trim orifice in the support housing is adjusted to provide the desired pressure drop across the functioning nozzle. Then, the valve cartridge is inserted in the support housing and sealed therein by welding/sealing the end closure cap onto the support housing to enclose the valve cartridge.